xfs: create new metadata UUID field and incompat flag
This adds a new superblock field, sb_meta_uuid. If set, along with a new incompat flag, the code will use that field on a V5 filesystem to compare to metadata UUIDs, which allows us to change the user- visible UUID at will. Userspace handles the setting and clearing of the incompat flag as appropriate, as the UUID gets changed; i.e. setting the user-visible UUID back to the original UUID (as stored in the new field) will remove the incompatible feature flag. If the incompat flag is not set, this copies the user-visible UUID into into the meta_uuid slot in memory when the superblock is read from disk; the meta_uuid field is not written back to disk in this case. The remainder of this patch simply switches verifiers, initializers, etc to use the new sb_meta_uuid field. Signed-off-by: NEric Sandeen <sandeen@redhat.com> Reviewed-by: NBrian Foster <bfoster@redhat.com> Signed-off-by: NDave Chinner <david@fromorbit.com>
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